The invention relates to a radio frequency device including a power amplifier circuit having an input and an output for radio frequency signals and having DC supply terminals, and including a power stabilizer circuit for controlling variations of the power of the radio frequency output signal of the power amplifier as a function of variations of a reference voltage.
The invention also relates to a mobile transceiver terminal including such a device, and, more particularly, a cellular mobile terminal.
It will be recollected that in a mobile transceiver terminal it is necessary to associate to the transceiver circuit a circuit that makes it possible to let the transmit power vary within limits as a function of a variable reference voltage. Actually, a mobile transceiver terminal cooperates with a base station whose distance to the mobile terminal varies when the user of the mobile terminal moves about. The transmit power of the mobile terminal depends on this distance for the base station to have a proper reception. A protocol generated by the base station is capable of informing the mobile terminal of the proper power level that the transmission system of the mobile terminal is to produce to avoid the saturation of the receiving system of the base station, taking this distance into account. The mobile terminal is thus to comprise a control circuit for controlling the transmitted power, so that this power corresponds to the proper power required by the base station.
A cellular mobile terminal is nowadays a consumer transceiver device which the conceiver of ideas seeks to make as light as possible and also as inexpensive as possible for an attractive, current and easy use. The circuits accommodated in the housing of the mobile terminal are thus to be small, inexpensive and highly reliable.
From the publication: xe2x80x9cIntegrated Circuit Technology Options for RFICs-Present Status and Future Directionsxe2x80x9d, pages 387-389, in IEEE journal of SOLID-STATE CIRCUITS, vol. 33, no. 3, March 1998, by Lawrence E. Larson, a device has already been known to include a power stabilizer of a power amplifier circuit that operates via the DC supply voltage control. This device comprises a power amplifier circuit whose output is connected by a coupler to an antenna and a power detector. This device further includes a control amplifier which receives an external DC control voltage called reference voltage and which applies a DC reference voltage to a stage that produces the DC supply voltage. The power detector also applies an input voltage to the control amplifier. Thus, the supply voltage of the power amplifier is slaved by a loop to a value so that there is agreement between the information produced by the power detector and the reference voltage that corresponds to the control voltage. In a mobile terminal, the control voltage is received by a processor which repeats the reference voltage transmitted by the base station.
A problem is that this device including the stabilizer circuit and power amplifier circuit generally has a poor performance due to the dispersions when the circuit elements are manufactured. More particularly, the power amplifier has highly dispersed characteristic features. By way of example, certain amplifiers can produce a power of 1 W, whereas other power amplifiers can produce a power of 1.5 W for the same DC supply voltage. Another problem is that this device needs the presence of a coupler which is a bulky and not very reliable element. Owing to these problems, this known device is not very suitable for use in a mobile terminal.
It is an object of the invention to provide a device that includes a power stabilizer circuit for a power amplifier circuit and does not have these problems. More particularly, it is an object of the present invention to provide a device whose output power is independent of the manufacturing dispersion of the circuit elements and which does not need the use of a coupler.
This object is achieved and the problems are solved with a device that is based on the evaluation of the efficiency of the power amplifier which is a stable characteristic feature, slightly affected by the manufacturing dispersions of the power amplifier. As a result, there is the advantage that the output power of the amplifier is well controlled. Moreover, this device offers the advantage of being simple and compact.